Metallic silver has been widely used as a recording material and a material of printing plate, and also as a highly conductive material because of its excellent electrical conductivity.
As a general method for producing metallic silver to date, for example, a method of using silver salts of organic acid, such as silver behenate, silver stearate, silver α-ketocarboxylate and silver β-ketocarboxylate, has been disclosed. For example, silver β-ketocarboxylate rapidly forms metallic silver even when subjected to a heat treatment at a low temperature of about 210° C. or less (see Patent Document 1). A method of forming metallic silver has been disclosed by taking advantage of such an excellent property and by dissolving silver β-ketocarboxylate in a solvent to prepare a silver ink composition, printing it on a substrate, and subjecting the resulting printed material to a heat (baking) treatment (see Patent Document 1).
On the other hand, for the heat treatment at the time of forming metallic silver, further reduction in the heating temperature has been expected. The reasons for this are that because, as the heating temperature reduces, the number of restrictions concerning the material of the substrate for printing the silver ink composition and carrying out a heat treatment is reduced, a substrate made of a material that is not highly heat resistant can also be used, and the range of use of the silver ink composition greatly expands. For example, in the case of using such a material that is not highly heat resistant for the housing of a communication device, the degree of freedom of design of the communication device is dramatically improved, such that it becomes possible to use a portion of the housing as a substrate for electronic circuits.
On the other hand, a method of forming a metallic silver coating film by applying a liquid composition formed by mixing silver formate and an amine compound onto a substrate and carrying out a heat treatment at 90° C. has been disclosed (see Patent Document 2).